1. Field of the Invention
This invention relates to the furnace process for producing carbon black from a carbon producing feedstock oil and to a feedstock injection assembly useful in the practice thereof.
2. Description of the Prior Art
The oil furnace process for obtaining high abrasion resistant carbon blacks for rubber reinforcing applications, particularly automotive tires, known in the relevant industry as the HAF, ISAF and SAF types, basically consists of contacting atomized droplets of a normally liquid hydrocarbon feedstock with an extremely turbulent mass of combustion products resulting from burning a mixture of fuel gas and excess pre-heated air. In accordance with the foregoing method, a major portion of the feedstock is pyrolytically dissociated in a partial oxidation reaction to provide a substantial yield of carbon black in the form of an aerosol from whence pulverulent carbon black is recovered and then pelleted.
Beyond the particle size requirement of the respective grades of carbon black mentioned, there are other important quality standards that must be met, foremost of which is structure. Structure is essentially the inherent tendency of the nascent carbon black particles to agglomerate to form chain-like units of the particles during and immediately subsequent to the completion of the pyrolysis reaction. The structure characteristic is very important insofar as it relates directly to certain critical properties exhibited by cure, carbon black reinforced rubber compositions. It will suffice to say, however, that the carbon black manufacturing art as presently practiced is highly sophisticated and thus those skilled in this art are well aware of the combination of processing parameters needed to provide a quality product.
Lately, however, an additional quality standard for tread grade rubber reinforcing carbon black has been assuming importance. Such concerns the particle size distribution of the resultant product. Essentially the improvement being sought in this regard is to produce a product composed of more uniform particle sizes and particularly, the elimination of the larger particle size component associated with the heretofore standard products. In this connection, particle size refers to the size of the resultant agglomerates. These new products are referred to as high tint blacks, named so because of the empirical test method utilized to measure this property.
It is known in the art that the manner whereby the feedstock is injected into the furnace, specifically at or near the center of the situs of maximum turbulency of the cracking gases, leads to the formation of high tint black. However, this expedient results in a product having unacceptably low structure properties. In order to increase structure, the feedstock injector can be moved upstream of the high turbulence zone to provide for a broader feedstock spray pattern as it enters the high turbulence zone. This unfortunately reduces tint by increasing the agglomerate size distribution, so to compensate the reaction time must be shortened. This practice, however, reduces yield and calls for an expensive drying operation to rid the final product of unreacted oil so that the carbon black will meet the stain test imposed by the consuming rubber industry. It is, accordingly, the object of this invention to provide a modification of the oil furnace process for producing high tint carbon black without experiencing the shortcomings mentioned above.